1. Field of Invention
The present invention relates generally to high-speed aircraft, and more particularly to long range supersonic cruise aircraft having sonic boom shock suppression capabilities.
2. Description of the Related Art
When an object such as an airplane travels through air, the movement of the plane causes a pressure disturbance that moves at the speed of sound. By way of example, the sound waves created by the nose of the plane will travel in an outward direction away from the aircraft. The air ahead of the plane receives the sound waves before the arrival of the aircraft, so that when the aircraft arrives, the air flows around the plane. As the airplane approaches the speed of sound, the sound waves merge closer and closer together at the front of the plane. When the aircraft is moving at the speed of sound the sound waves merge together into a “shock wave” which is an almost instantaneous line of change in pressure, temperature and density.
As shown in FIG. 1, an aircraft traveling at supersonic speed will generate a bow shock wave from the nose of the airplane and a tail shock wave created by the tail of the plane. The tail shock wave is created by an under pressurization in the air about the tail. The overall shock wave pressure gradient extends from an over-pressure area beneath the forward portion of the plane and an under-pressure area beneath the aft section of the aircraft, as shown in FIG. 1. Pressure disturbances coalesce into an N-wave shape that has the largest shock magnitudes at the inflection points 102, 104 of the pressure gradient curve. Since the front of a supersonic aircraft generates an increase in ambient pressure, and the rear generates a decrease in pressure, a corresponding variation in propagation speed causes aircraft pressure disturbances to stretch out as they propagate to the ground. As the disturbances stretch out, they also tend to coalesce because shocks waves travel only halfway between the speed of the lower pressure ahead and higher pressure behind.
The shock waves travel through the atmosphere to the ground. To an observer, the shock waves are felt as an abrupt pressure compression, followed by a gradual pressure decompression and a final abrupt recompression to ambient pressure. The abrupt change in pressure can create a disturbingly loud sound. Additionally, the shock waves may cause structural damage to surrounding buildings. For these reasons supersonic transports (SST) have been limited to routes that do not carry the plane across land. SSTs are therefore restricted to flights across water, thereby limiting the usefulness of the planes. It is desirable to reduce the effects of sonic shock waves created by supersonic aircraft.